Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$142.34	9.188%	$155.4182	$155.42	$155.40	$155.40
Purchase #2	$38.96	10.390%	$43.0079	$43.01	$43.00	$43.00
Purchase #3	$158.79	7.133%	$170.1165	$170.12	$170.10	$170.10
Purchase #4	$228.53	13.254%	$258.8194	$258.82	$258.80	$258.80
Purchase #5	$134.94	10.376%	$148.9414	$148.94	$148.95	$148.90
Purchase #6	$107.58	6.606%	$114.6867	$114.69	$114.70	$114.70
Purchase #7	$88.63	13.376%	$100.4851	$100.49	$100.50	$100.50
7 purchase totals =	$899.77		$991.4752	$991.49	$991.45	$991.40